I want to use these for my rear and center surrounds in my 6.1 system. Of course the budget does not allow me to buy 3 QS8 speakers as I wish I could. Would a pair of QS8s in the rear w/ a QS4 center rear be OK or should I just stick with 3 QS4s? My room is 23' x 19'with the system set up using about 70% of that space. (up front B&W 602 and SVS 25-31 sub w/ Denon 1803)